SRS Transmission Timing in Shared Spectrum After LBT Failure
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Solution Overview
Problem
In wireless communications systems using shared radio frequency spectrum, the likelihood of successful listen-before-talk (LBT) procedures for sounding reference signal (SRS) transmissions is low, leading to inaccurate channel quality metrics and reduced network efficiency and capacity due to failed LBT procedures and persistent interference.
Innovation Solution
Implementing techniques that enhance LBT success by allowing multiple SRS transmission times within a periodic interval, using randomly selected timing offsets, aperiodic SRS transmissions, and varying cyclic prefix lengths based on channel occupancy time, and employing different LBT procedures for different transmission times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a UE performs LBT procedure prior to SRS transmission in shared radio frequency spectrum, then the transmission can avoid interference with other devices, but the likelihood of successful transmission decreases due to channel unavailability
Solution Approach 1:
The patent implements dynamic SRS transmission timing where the UE can adjust transmission opportunities based on LBT outcomes. Multiple configured transmission times within periodic intervals allow the system to adapt to changing channel conditions, switching between transmission and non-transmission states based on LBT success, thereby resolving the contradiction between interference avoidance and transmission reliability
Solution Approach 2:
The base station configures multiple SRS transmission time instances in advance within periodic intervals before the actual transmission occurs. This preliminary configuration of multiple opportunities allows the UE to have pre-planned fallback options, ensuring that if the first LBT attempt fails, subsequent transmission opportunities are already prepared, thus maintaining reliability while respecting interference avoidance requirements
2Reliability
If multiple SRS transmission opportunities are configured within periodic intervals, then the likelihood of successful LBT increases, but the system complexity increases
Solution Approach 1:
The patent varies cyclic prefix lengths based on whether the SRS transmission occurs within or outside the base station's channel occupancy time. This parameter change provides a simple yet effective mechanism to differentiate transmission types and manage multiple opportunities without requiring complex configuration, as the cyclic prefix length automatically adapts to the transmission context, reducing overall system complexity while maintaining high LBT success probability
Solution Approach 2:
The SRS periodic interval is segmented into multiple discrete transmission time opportunities rather than a single transmission point. This segmentation divides the transmission window into manageable segments, each with its own LBT attempt, allowing the system to achieve higher success probability through multiple tries while keeping each individual configuration element simple and manageable
3Productivity
If cyclic prefix length is varied based on channel occupancy time, then transmission efficiency is improved, but the configuration complexity increases
Solution Approach 1:
The patent changes the cyclic prefix length parameter based on the channel occupancy time context - using longer cyclic prefix for transmissions outside channel occupancy time and shorter cyclic prefix for transmissions within channel occupancy time. This parameter change optimizes transmission efficiency by adapting to channel conditions without requiring complex configuration mechanisms, as the cyclic prefix length is directly tied to the temporal context of the transmission opportunity
Solution Approach 2:
Different cyclic prefix lengths are applied locally based on the specific transmission context - whether the transmission occurs within or outside the base station's channel occupancy time. This local quality approach allows optimization for each specific transmission opportunity based on its temporal characteristics, improving overall efficiency while keeping the configuration rule simple and context-dependent rather than globally complex
Data Source
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AI summary
Methods, systems, and devices for wireless communications are described for managing sounding reference signal (SRS) transmissions in shared radio frequency spectrum. Described techniques provide for increased occasions at which a SRS may be transmitted, enhance likelihood of a successful listen-before-talk (LBT) procedure, or any combinations thereof. Increased occasions for SRS may be provided through multiple transmission times that are available in the event of an earlier LBT failure. Enhanced likelihood of successful LBT may be provided through one or more timing offsets that may be randomly selected from a set of available timing offsets, selection of a cyclic prefix length for a SRS based on whether the SRS transmission is within or outside of a channel occupancy time of a base station, providing an initial SRS transmission time for an initial periodic time interval, triggering of an aperiodic SRS within the channel occupancy time, or any combinations thereof.